System and method for stabilizing the human spine with a bone plate

ABSTRACT

A spinal plate system and method for fixation of the human spine is provided. In an embodiment, the spinal fixation system includes a plate, a coupling member, a locking system for substantially locking the coupling member in a desired position, and an anchoring system to secure the coupling member in the locking system. The plate may have a hole that allows the coupling member to couple the plate with a bone. At least a portion of the coupling member may swivel in the hole so that a bottom end of the member may extend at a plurality of angles substantially oblique to the plate. The locking system may lock the coupling member in desired positions relative to the plate. The anchoring system may secure the coupling member in the locking system to inhibit the coupling system from detaching from the locking system when stressed. An assembly tool may be used to engage and disengage the anchoring system during the installation or removal of the spinal fixation system.

This is a continuation of allowed U.S. patent application Ser. No.10/015,206, filed Nov. 19, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to spinal fixation systems andthe like. The present invention also generally relates to a spinal platesystem that includes a mechanism for fixably attaching heads offasteners to a spinal plate.

2. Description of the Related Art

The use of spinal fixation plates for correction of spinal deformitiesand for fusion of vertebrae is well known. Typically, a rigid plate ispositioned to span bones or bone segments that need to be immobilizedwith respect to one another. Bone screws may be used to fasten the plateto the bones. Spinal plating systems are commonly used to correctproblems in the lumbar and cervical portions of the spine, and are ofteninstalled posterior or anterior to the spine.

Spinal plate fixation to the cervical portion of the spine may be riskybecause complications during surgery may cause injury to vital organs,such as the brain stem or the spinal cord. When attaching a fixationplate to a bone, bone screws are placed either bi-cortically (i.e.,entirely through the vertebrae such that a portion of the fastenerextends into the spinal cord region) or uni-cortically (i.e., thefastener extends into but not through the vertebrae). Uni-corticalpositioning of bone screws has grown in popularity because it isgenerally safer to use. Bi-cortical fasteners are intended to breach thedistal cortex for maximum anchorage into the bone; however, thisplacement of the fasteners may place distal soft tissue structures atrisk. Fastener placement is particularly important in anterior cervicalplate procedures because of the presence of the spinal cord opposite thedistal cortex. Unfortunately, uni-cortical fasteners may move from theirdesired positions because of the soft texture of the bone marrow. Infact, the portion of the bone surrounding such fasteners may fail tomaintain the fasteners in their proper positions. The result is backoutof the fastener.

Backout of the fastener is particularly problematic when two fastenersare implanted perpendicular to the plate. When the fasteners are placedin such a manner, backout may occur as a result of bone failure over aregion that is the size of the outer diameter of the fastener threads.To overcome this problem, two fasteners may be angled in converging ordiverging directions with respect to each other within the bone. Theamount of bone that is required to fail before backout may occur isincreased by this configuration as compared to fasteners that areimplanted in parallel. Although positioning convergent or divergentfasteners in a bone reduces the risk of backout, backout may stilloccur.

Backout may damage internal tissue structures and cause complications ifthe dislocated fastener penetrates the tissue structures. For example,if backout occurs, the fastener might breach the esophageal wall of thepatient. Such a breach may permit bacterial contamination of surroundingtissues, including the critical nerves in and around the spinal cord.Such a breach could be fatal.

In an attempt to reduce the risk of damage to internal tissuestructures, some cervical fastener plate systems have uni-corticalfasteners that attach both to the bone and to the plate. If a fastenerdoes backout, the fastener remains connected to the plate so that itdoes not contact internal tissue structures. U.S. Pat. No. 5,364,399 toLowery et al. describes one such system and is incorporated by referenceas if fully set forth herein. The Lowery et al. plating system includesa locking fastener at each end of the plate. The locking fastenerengages the head of the bone screw to trap the fastener within a recessof the plate. Since the locking fastener is positioned over portions ofthe bone screws, the locking fastener may extend above the upper surfaceof the plate. Thus, the locking fastener may come into contact withinternal tissue structures, such as the esophagus.

Another plating system that includes a fastener-to-plate lockingmechanism is the Aline™ Anterior Cervical Plating System sold by Smith &Nephew Richards Inc. in Memphis, Tenn. A description of this system canbe found in the Aline™ Anterior Cervical Plating System SurgicalTechnique Manual by Foley, K. T. et al., available from Smith & NephewRichards Inc., 9/96, pp. 1-16 and is incorporated by reference as iffully set forth herein. The bone screws of this system have openingswithin each bone screw head for receiving a lock fastener coaxiallytherein. Each bone screw may be inserted into a bone such that the headof the fastener is positioned within a hole of a plate placed adjacentto the bone. The head of each bone screw is slotted so that portions ofthe head are deflected toward the plate during insertion of the lockfastener within the opening of the bone screw. Positioning and insertinga lock fastener within the opening can be difficult due to the smallsize of the lock fastener. The surgeon may be unable to hold onto thelock fastener without dropping it. If a lock fastener falls into thesurgical wound, it may be difficult to retrieve. In some instances, thelock fastener may be unretrievable.

SUMMARY OF THE INVENTION

An implant system may be used to immobilize a portion of a human spine.The implant system may include a plate comprising end holes, midlineholes, fasteners, and expandable/contractible rings. The fasteners andrings may include mechanisms for anchoring or locking the fastener headswithin the rings to inhibit backout of the fastener.

The end holes extend from an upper surface to a lower surface of theplate. The end holes may be disposed in pairs at opposite ends of theplate. Each end hole receives at least a portion of a head of afastener. Herein, “fastener” means any elongated member, threaded ornon-threaded, which is securable within a bone. Fasteners include, butare not limited to screws, nails, rivets, trocars, pins, and barbs. Thefastener may be a bone screw. A fastener may have a fastener head. Thefastener head typically includes an opening adapted to mate with a tool.The tool allows the insertion of the fastener into a bone. Each end holemay also be spherically contoured to permit the fastener to be“obliquely angulated” relative to the plate. Herein, “obliquelyangulated” means that the fastener may be positioned throughout a widerange of angles relative to an axis that is perpendicular to the plate.Obliquely angulating a fastener into a bone may reduce the risk ofbackout of the fastener.

The expandable/contractible rings may be sized so that a ring seatswithin an end hole between the plate and the fastener. The inner surfaceof each ring may be shaped to mate with a fastener head while the outersurface may be shaped to mate with the inside surface of an end hole.The outer surface of each fastener head may be tapered so that an upperportion of the head is larger than a lower portion of the head. Theinner surface of the ring may have a taper that generally corresponds tothe taper of the fastener head.

Each ring may also have a gap that extends vertically through the ringto make the ring more readily expandable and contractible. Duringinsertion of the fastener head into the ring, the fastener head exertsforce against the ring to expand the ring against the inner surface ofthe hole. Expanding the ring against the inner surface of the hole maysecurely fix the fastener to the plate.

The fastener head and the ring may include a locking mechanism to attachthe fastener head to the plate. The locking mechanism may inhibitbackout of the fastener head from the ring if the fastener loosens inthe bone. The locking mechanism may also inhibit the fastener head fromcontacting adjacent tissue structures since the locking mechanismattaches the fastener head to the plate. In some embodiments, there istolerance for some freedom of movement in an axial direction between alocking mechanism and a fastener head. The availability of some axialmovement may allow the fastener to back out or loosen slightly from thebone during a normal period of adjustment after implantation of a spinalfixation system.

Midline holes may be formed through the plate at various locations alonga midline axis extending across the plate. The surface of the plate thatsurrounds each midline hole may be tapered. Further, the heads offasteners that may be positioned within the plates may have taperedouter surfaces that generally correspond to the tapered surface of theplate. Thus, when such a fastener head is inserted into a midline hole,the shape of the plate causes the fastener to become fixably attached tothe plate in a position that is substantially perpendicular to theplate. Midline holes may be used to attach a bone graft to the boreplate. Oblique angulation of fasteners positioned within the midlineholes may not be required.

The bone plate may have one or more spikes located on the surface of theplate that faces the spinal column. Spikes may be disposed in pairs atopposite ends of the plate proximate the end holes. The spikes may betapped into the bone to help inhibit the bone plate from slipping duringsurgical implantation.

Prior to surgical implantation of the spinal plate system, theexpandable/contractible rings may be placed within the end holes of theplate. The plate may then be positioned adjacent to a portion of thespine that requires spinal fixation. Holes may be drilled and/or tappedat desired angles into portions of the bone underlying the end holes ofa plate. Fasteners may be inserted through the end holes into the holesin the bone. The heads of the fasteners may be positioned within the endholes such that the rings surround at least a portion of the heads. Therings may lock the fasteners in place without occupying regions outsideof the end holes. Further, since the rings are pre-positioned within theend holes, surgeons do not have to worry that they may drop the ringsduring insertion of the rings into the end holes of the plate.

In one embodiment, a locking mechanism secures a fastener head to aring. A locking mechanism may have a top and one or more flexible armsthat angle downwards and outwards from the top. The ends of the armshave prongs that are substantially parallel to the top of the lockingmechanism. A locking mechanism in a compressed configuration, fits intoan opening formed in the head of a fastener. The prongs of the lockingmechanism fit within holes located near the bottom of the opening. Theholes extend from the outer surface of the head to the opening. When theprongs are positioned in the holes, the prongs extend through the holesso that the locking mechanism is in an extended configuration. Theprongs that extend out of the head of the fastener fit within a grooveon the inner surface of the ring to enhance the connection between thefastener and the ring.

The locking mechanism may be inserted in the fastener head prior to thesurgical procedure to avoid the risk of dropping the locking mechanismduring the surgical procedure. An insertion and extraction tool retractsthe prongs on the locking mechanism into the head during insertion orextraction of a fastener. The tool may include a handle, a shaft, and ahollow driver head shaped to match a drive section of the opening on thefastener head. Inserting the driver head into the opening slides thehead over the locking mechanism and compresses the shafts of the lockingmechanism. Compressing the shafts of the locking mechanism retracts theprongs into the fastener head. To insert a fastener into a bone, theuser inserts the fastener into the bone until the head is fully insertedin the ring. Removing the driver head from the opening causes the shaftsof the locking mechanism to expand outwards so that the prongs extendout of the holes into the fastener head.

To remove a fastener that has a locking mechanism, the user inserts thedriver head of the insertion and extraction tool into the opening of thefastener head. The driver head compresses the shafts of the lockingmechanism and causes the prongs to retract within the fastener head. Theuser may then remove the fastener from the bone.

In another embodiment, a tapered fastener head locks into a ring by oneor more fingers on the ring that snap into grooves on the fastener head.L-shaped slots cut into the top of the ring may define the fingers. Thefingers have springlike action so that the fingers snap into the grooveson the fastener head when a fastener head is inserted into the ring. Asthe fastener head passes into the ring, the tapered outer surface of thehead expands the ring against the inner surface of the plate. When thegroove on the fastener head reaches the fingers, the fingers snap intothe groove, fixing the fastener in the ring and helping to inhibitbackout.

In another embodiment, a fastener head locks to a ring by one or moreridges on the ring that snap into grooves on the fastener head. Notchescut into the top of the ring may form paddles. A ridge may extend alongan inside surface of each paddle proximate the top of the ring. Thepaddles have a springlike action so that the ridges snap into thegrooves on the fastener head during insertion of the fastener head intothe ring. The ridges of the ring residing within a groove of thefastener head may fix the fastener in the ring and help inhibit backoutof the fastener.

An extraction tool module fits over an insertion tool and allows theretraction of the ring ridges from the fastener head. The insertion toolincludes a handle, a shaft, and a driver head shaped to match theopening on the fastener head. The extraction module slides over theshaft of the insertion tool. The extraction module may include a handleand an extraction head. The extraction head may include a tip thatslides over the fastener head and contacts the ends of the paddles. Theouter surface of the tip tapers. As the extraction module is pusheddown, the tapered surface of the tip forces the paddles outwards anddisengages the ridges on the paddles from the grooves on the fastenerhead. Disengaging the ridges on the paddles from the grooves on thefastener head allows the fastener to be backed out of the bone.

Using a locking mechanism between the fastener head and the ring mayresult in a strong connection between the fastener and the plate. Evenif the shank of a fastener loosens within the bone, the fastener headwill tend to remain within the hole of the plate so as not to protrudefrom the plate into surrounding body tissue. Allowing some axial freedomof movement for the fastener head in the ring may allow the fastener toback out slightly during an adjustment period after installation of thespinal fixation system.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art with the benefit of the following detaileddescription of embodiments and upon reference to the accompanyingdrawings in which:

FIG. 1 is a top view of an embodiment of a spinal plating system thatmay be used for fixation of the human spine.

FIG. 2 is a partial cross-sectional view of the spinal plating systemtaken substantially along line 2-2 of FIG. 1. The fastener is not shownin section.

FIG. 3 is a partial cross-sectional view of the spinal plating systemtaken substantially along line 3-3 of FIG. 1, wherein the fasteners arein a converging orientation within end holes of a plate. The fastenersare not shown in section.

FIG. 4 is a partial cross-sectional view of the spinal plating systemtaken substantially along line 4-4 of FIG. 1, wherein the fasteners arein a diverging orientation within end holes of a plate 5, the fastenersare not shown in section.

FIG. 5 depicts an embodiment of a fastener with grooves and holes toengage a locking mechanism.

FIG. 6 is a partial front view of a fastener with holes in the fastenerhead.

FIG. 7 is a top view of a fastener head having grooves for engaging alocking mechanism.

FIG. 8 is a top view of an embodiment of a fastener head with ahexagonal opening and holes to engage a locking mechanism.

FIG. 9 is a perspective view of a locking mechanism.

FIG. 10 is a perspective view of a ring that may be used with a fastenerand a locking mechanism.

FIG. 11 is a partial sectional view of an insertion/extraction tool forfasteners with locking mechanisms.

FIG. 12 a is a bottom view of a driver head of the insertion/extractiontool shown in FIG. 11. The tool may be used with the fastener head shownin FIG. 7.

FIG. 12 b is a bottom view of the driver head of the insertion andremoval tool shown in FIG. 11 which may be used with the fastener headshown in FIG. 8.

FIG. 13 is a sectional view of a fastener head with aninsertion/extraction tool and compressed locking mechanism during aninsertion process.

FIG. 14 is a sectional view of a fastener head and locking mechanisminserted into a ring.

FIG. 15 is a perspective view of an embodiment of a fastener.

FIG. 16 is a front view of an embodiment of a fastener head.

FIG. 17 is a perspective view of an embodiment of a fastener.

FIG. 18 is a front view of an embodiment of a fastener head with agroove.

FIG. 19 is a perspective view of an embodiment of a ring.

FIG. 20 is a perspective view of an embodiment of a ring.

FIG. 21 is a perspective view of an embodiment of a ring.

FIG. 22 is front view of an insertion/extraction tool which may be usedwith the ring of FIG. 21.

FIG. 23 a is a partial cross sectional view of a fastener duringinsertion in the ring of FIG. 21. The shaft of the insertion/extractiontool is not shown in cross section.

FIG. 23 b is a partial cross sectional view of a fastener afterinsertion in the ring of FIG. 21. The shaft of the insertion/extractiontool is not shown in cross section; and

FIG. 23 c is a partial cross sectional view of a fastener during removalfrom the ring of FIG. 21. The shaft of the insertion/extraction tool isnot shown in cross section.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but to the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, and particularly to FIG. 1, a spinal platingsystem is designated generally as 20. The spinal plating system 20 maybe used to correct problems in the lumbar and cervical portions of thespine. For example, the plating system 20 may be implanted into theocciput bone that is located at the base of the skull. The platingsystem 20 may also be installed anterior to the spine. The spinalplating system 20 includes plate 22 that is placed adjacent to a portionof the spine and spans at least two vertebrae. Plate 22 may include fourend holes 24, located at corners of the plate. End holes 24 passvertically through plate 22 such that the holes extend from an uppersurface 26 to a lower surface 28 of the plate as depicted in FIG. 2. Endholes 24 are configured to receive rings 30. Fasteners 32 fit within therings 30. Herein, “fastener” means any elongated member, threaded ornon-threaded, which is securable within a bone. Fasteners include, butare not limited to screws, nails, rivets, trocars, pins, and barbs. Thefastener may be a bone screw. Rings 30 fixedly attach fastener heads 34of fasteners 32 to plate 22. Gap 36 may exist in each of the rings 30. Agap 36 allows for expansion and contraction of a ring 30. Ringcontraction allows a ring 30 to be easily inserted into an end hole 24of the plate 22.

The spinal plating system 20 may also include one or more central holes38 that extend vertically through plate 22. One of the central holes 38may be located at about the mid-point of the plate 22. Head 40 offastener 42 is positioned within one of the central holes 38. Multiplecentral holes 38 provide a surgeon with options as to the most desirablelocation for placement of a fastener 42. Fastener 42 may be used toconnect plate 22 to a bone graft (not shown).

FIG. 2 shows a fastener 42 within one of the central holes 38 of plate22. Fastener 42 may include head 40 and shank 44. The shank 44 extendsfrom the base of head 40. In one embodiment, the inner surface of acentral hole 38 tapers so that the hole is larger at upper plate surface26 than at the lower plate surface 28. The outer surface of the fastenerhead 40 has a taper that generally corresponds to the taper of thecentral hole 38. During implantation of a fastener 42 into a bone graft,the shank 44 of the fastener 42 is inserted into a hole that has beenformed in the bone graft under hole 38. Because the lower portion ofhole 38 is smaller than the upper portion of the fastener head 40,fastener 42 may become locked into place within the central hole 38 oncethe fastener has been inserted to a desired depth within the bone graft.The bone plate 22 may have spikes 45 extending from the lower platesurface 28.

As shown in FIG. 2, the plate 22 may have a curvature. The curvature mayenhance fixation of the plate 22 to a bone. The bone plate 22 may haveone or more spikes 45 located on the surface of the plate that faces thebone. The spikes 45 may be disposed in pairs at opposite ends of theplate proximate the end holes 24. The spikes 45 may be tapped into thebone to help inhibit the bone plate 22 from slipping during surgicalimplantation.

FIG. 3 depicts a cross-sectional view of an embodiment of a finalplating system 10 wherein a pair of fasteners 32 are in a convergingconfiguration. FIG. 4 depicts a cross-sectional view of an embodiment ofa spinal plating system wherein a pair of fasteners 32 are in adiverging configuration. Ring 30 fits into a hole 24 between plate 22and fastener head 34. Inner surfaces 46 of holes 24 may have arcuate orspherical contours. Outside surfaces 48 of rings 30 may have arcuate orspherical contours that substantially correspond to the contours of theinner surfaces 46 of the holes 24. Having a contoured ring outer surface48 that substantially corresponds to the contour of the inner holesurface 46 allows a ring 30 positioned in a hole 24 to be capable ofpolyaxial rotation within the end hole 24.

The combination of ring 30 within end hole 24 functions like a ball andsocket since the ring may be swiveled or polyaxially rotated within theend hole. The ability of the ring 30 to rotate polyaxially within theend hole 24 allows a fastener 32 to be positioned through the plate 22at various angles with respect to an axis that is perpendicular to theplate. FIGS. 3 and 4 show angle A for particular fastenerconfigurations. The angle A is defined between the longitudinal axis 50of the fastener 32 and imaginary axis 52 that is perpendicular to theplate 22. The angle A may range from 0 to about 45 degrees, preferablyfrom about 0 to about 30 degrees, and more preferably from 0 to about 0and 15 degrees.

Fasteners 32 may also be set in positions such that the fasteners arenon-planar with respect to a latitudinal plane extending through plate22. For example, one fastener 32 may be positioned out of the page andanother fastener 32 may be positioned into the page, as depicted inFIGS. 3 and 4. Fasteners 32 set in diverging or converging directions inthe end holes 24 may reduce the possibility of backout. Further, the useof rings 30 to fixedly attach fasteners 32 to plate 22 may inhibitdamage to tissue structures by any fasteners that do loosen within abone, since such fasteners would remain attached to the plate 22.Fasteners 32 may be placed in uni-cortical positions within a bone sincethe problem of fastener backout is reduced by having obliquely angulatedfasteners in converging or diverging configurations.

Ring 30 may at least partially surrounds head 34 of fastener 32positioned within end hole 24. A shank 54 of fastener 32 may includethreading 56 to allow the fastener to be inserted into a bone whenfastener 32 is rotated. As depicted in FIG. 1, fastener head 34 mayinclude a cavity 58 that extends from the top of the head to an innerportion of the head. Cavity 58 may be shaped to receive an end of a toolthat inserts or removes the fastener 32 from a bone. The tool end may bein the form of a hex wrench, a star wrench or a screwdriver blade.

Inner surface 60 of ring 30 and outer surface 62 of head 34 may havemating tapered surfaces, as depicted in FIG. 3 and FIG. 4. In oneembodiment, the bottom portion of head 34 may be smaller than the upperportion of an unstressed ring 30, while the upper portion of the headmay be larger than the upper portion of the ring. As fastener 32 isinserted into a bone, head 34 applies a radial force to ring 30 whichcauses the ring to expand within the end hole 24. Expanding the ring 30increases the size of gap 36 and may cause the outside surface 46 of thering to abut against inner surface 46 of the end hole 24. Aninterference fit forms between fastener head 34, ring 30, and plate 22in which these elements fit together such that each element obstructsthe movement of the other elements. Hoop stress of ring 30 on head 34fixedly attaches fastener 32 to plate 22.

Ring 30 may be capable of swiveling within a hole 24 so that one portionof ring 30 is adjacent to the upper surface 26 of bone plate 22 whileanother portion of the ring lies adjacent to the lower surface 28 of thebone plate. In one embodiment, ring 30 may sufficiently thin to residewithin end hole 24 without extending beyond the upper or lower surface26, 28 of bone plate 22. The ring 30 and fastener head 34 remain withinend hole 24 so that the spinal plating system 20 may have a minimalprofile width. Having rings 30 and the fastener heads 34 which do notextend above the upper surface 26 or below the lower surface 28 of plate22 may prevent the rings and heads from contacting adjacent tissuestructures. In other embodiments, however, fasteners 32 may be capableof being angulated relative to bone plate 22 such that the rings 30extend from the end holes 24 beyond upper and/or lower surfaces of thebone plate.

In one embodiment, the spinal plating system 20 is prepared for surgicalimplantation by positioning rings 30 within end holes 24. During thesurgical procedure, holes may be drilled and tapped into the bones towhich plate 22 is to be attached. Plate 22 may then positioned adjacentto the bones and over the holes in the bone. Fasteners 32 may be placedthrough a ring 30 and into the bone holes. Each fastener 32 may beobliquely angulated into the plate 22. The fasteners 32 may be insertedinto the bone until the fastener heads 34 expand the rings 30 againstthe inner surfaces 46 of the holes 24; thus fixing the fasteners to therings, and the rings to the plate 22. If necessary, a fastener 42 may bepositioned in one of the central holes 38.

In one embodiment, ring 30 has an outer width that is less than or aboutequal to the width of an end hole 24 in bone plate 22 at a locationbetween an upper surface 26 and lower surface 28 of the bone plate. Thewidth of each end hole 24 proximate the upper and lower surfaces 26, 28of bone plate 22 is less than or about equal to an outer width of ring30. The width of the ring may inhibit a ring positioned in a hole fromfalling out of the hole. Prior to surgery, a ring 30 may be positionedwithin each end hole 24 of bone plate 22. When seated within hole 24,ring 30 may be capable of swiveling within the hole, but the ring isinhibited from falling out of the hole because of reduced width of thehole proximate the upper and lower surfaces 26, 28 of the plate 22. Asurgeon may use a bone plate 22 having rings 30 positioned within holes24 prior to surgery. Alternatively, rings 30 may be manually positionedwithin holes 24 during surgery.

Texturing the outer surface 48 of a ring 30 or an inner surface 46 of ahole 24 may further inhibit movement of a fastener 32 with respect to abone plate 22. Both surfaces may be textured to more effectively inhibitmovement of a fastener 32 with respect to a bone plate 22. Duringmanufacturing procedures, the outer surface 48 of ring 30 and the innersurface of end hole 24 are formed as relatively smooth surfaces. Whilethe friction between these smooth surfaces tends to be sufficient tomaintain fastener 32 in a fixed position with respect to plate 22; understressful conditions ring 30 may rotate within hole 24. By providing atleast one textured surface, the coefficient of friction between hole 24and ring 30 is increased. The increase in friction between hole 24 andring 30 may help to inhibit fastener movement relative to plate 22.

Several types of textured surfaces may be used to increase thecoefficient of friction between ring 30 and hole 24. In general, anyprocess that transforms a relatively smooth surface into a texturedsurface having an increased coefficient of friction may be used. Methodsfor forming a textured surface include, but are not limited to: sanding,forming grooves within a surface, shot peening processes, electricdischarge processes, and embedding of hard particles within a surface.

A shot peening process for forming a textured surface is described inU.S. Pat. No. 5,526,664 to Vetter which is incorporated by reference asif set forth herein. In general, a shot peening process involvespropelling a stream of hardened balls, typically made of steel, at arelatively high velocity at a surface. To create a pattern upon an areaof the surface the stream is typically moved about the surface. Thespeed by which the stream is moved about the surface determines the typeof textured surface formed.

An electrical discharge process is based on the principle of removal ofportions of a metal surface by spark discharges. Typically a spark isgenerated between the surface to be treated and an electrode by creatingpotential differential between the tool and the electrode. The sparkproduced tends to remove a portion of the surface disposed between theelectrode and the surface. Typically, the electrode is relatively smallsuch that only small portions of the surface are removed. By moving theelectrode about the surface numerous cavities may be formed within thesurface. Typically these cavities are somewhat pyramidal in shape.Various patterns may be formed within the surface depending on how theelectrode is positioned during the discharge. Electric dischargemachines are well known in the art. A method for forming a frictionalsurface within a metal surface using an electric discharge process isdescribed in U.S. Pat. No. 4,964,641 to Miesch et al., which isincorporated by reference as if set forth herein.

Embedding hardened particles in a surface produces a textured surface. Amethod for embedding hardened particles in a metal surface is describedin U.S. Pat. No. 4,768,787 to Shira, which is incorporated by referenceas if set forth herein. The method of Shira involves using a laser orother high-energy source to heat the surface such that the surface meltsin selected areas. Just before the molten area re-solidifies, a streamof abrasive particles is directed to the area. In this manner some ofthe particles tend to become embedded within the molten surface. Theparticles typically have a number of sharp edges that protrude from thesurface after the particles have been embedded within the surface.

Any of the above methods of texturing may be used in combination withanother method. For example, the inner surface 46 of hole 24 may betextured using a pattern of grooves. The outer surface 48 of ring 30,however, may be textured using an electrical discharge method. Whencoupled together the textured surfaces of hole 24 and ring 30 mayinteract with each other to provide additional resistance to movement ofthe ring within the hole.

FIG. 5 illustrates an embodiment of fastener 100. The fastener 100 mayinclude fastener head 102, opening 104, optional grooves 106, holes 108,shank 110 and threads 112. Opening 104 accepts a drive tool, such asdrive tool 114, which is described below. The opening 104, grooves 106and holes 108 accept locking mechanism 116, as described below. Holes108 extend from the outer surface 118 of head 102 to the opening 104. Inone embodiment, the outer surface 118 is substantially cylindrical. Inanother embodiment, the head 102 tapers from a widest portion near theupper surface of the head to a narrowest portion near the shank 110.

FIG. 6 is a side view of the head 102 of an embodiment of fastener 100showing holes 108 and optional rim 120. Rim 120 may serve to limit theinsertion of fastener 100 into a ring 30 during use.

FIG. 7 is a top view of the head 102 of a fastener 100 with optionalgrooves 106. FIG. 8 shows an alternate embodiment of fastener 100 havinga hexagonal shape opening 104 and no grooves.

FIG. 9 illustrates a locking mechanism 116 used with fastener 100.Locking mechanism 116 includes top 122 with shafts 124 extendingdownwards and outwards from the top. Prongs 126 are located at ends ofshafts 124. Prongs 126 may be substantially parallel to each other andalso may be substantially parallel to the locking mechanism top 122. Theshafts 124 have a spring-like action which allows the shafts 124 to becompressed. The spring-like action also allows the shafts to return toan original configuration when not compressed.

FIG. 10 illustrates an embodiment of a ring 130 that may be used incombination with fastener 100 and locking mechanism 116. Ring 130includes groove 132. Groove 132 engages prongs 126 on locking mechanism116 to secure fastener 100 in ring 130 after insertion. Gap 36 in ring130 allows the ring to contract during insertion of the ring 130 into anend hole 24 of the bone plate 22. Gap 36 also allows ring 130 to beexpanded by the head 102 of fastener 100 in the ring 130 to abut thering against the inner surface 46 of the end hole 24. Abutting the ring130 against the inner surface 46 of the end hole 24 may fix the positionof fastener 32 relative to the bone plate 22.

FIG. 11 illustrates tool 114. The tool 114 may be used during theinsertion and extraction of a fastener 100 and locking mechanism 116.The insertion/extraction tool 114 includes a shaft 172. One end of shaft172 may include a handle 174 for turning the tool during insertion andremoval of a fastener 100. FIG. 11 shows a modified T-handle 174 coupledto the shaft 172, but any type of handle that allows torque to beapplied to the fastener during insertion and removal may be used. At anopposite end of shaft 172 from handle 174 is driver head 176. The outersurface of driver head 176 may be shaped to complement the shape ofopening 104 in the head of the fastener 100. Driver head 176 may beinserted into the opening 104 of the fastener 100. The fastener may beinserted in an end hole 24 of a bone plate 22 and into a bone byrotating insertion/extraction tool 114. Driver head 176 includes cavity178. The inner surface of the cavity may slide over and compress theshafts 124 and prongs 126 of a locking mechanism 116.

FIG. 12 a shows a bottom view of an embodiment of a driver head 176 ofan insertion/extraction tool 114. The driver head of FIG. 12 a may beused with the type of fastener head 102 shown in FIG. 7. The driver head176 has cavity 178 which allows the driver head to slide over andcompress a locking mechanism 116. The driver head 176 includes ridges180 for engaging complementary grooves 106 in the opening 104 of afastener head 102. FIG. 12 b shows an alternate embodiment of a driverhead 176 of an insertion/extraction tool 114. The driver head of FIG. 12b may be used with the type of fastener head 102 shown in FIG. 8. Thedriver head 176 has cavity 178 which allows the driver head to slideover and compresses a locking mechanism 116. The driver head 176 may behexagonal shaped to mate with opening 104 of a fastener head 102.

FIG. 13 shows a cross sectional view of an embodiment of a fastener 100,locking mechanism 116, and insertion/extraction tool 114 during theinsertion process. Driver head 176 inserts into opening 104 of fastenerhead 102. Shafts 124 of locking mechanism 116 are compressed withincavity 178 of driver head 176. The compression of shafts 124 causesprongs 126 to retract in holes 108, which allow fastener head 102 to beinserted into a ring 130 without interference by extended prongs 126.When insertion/extraction tool 114 is removed, the shafts 124uncompress, which causes the prongs 126 to extend out of holes 108.

FIG. 14 shows a cross sectional view of an embodiment of a fastener 100,locking mechanism 116, and ring 130 after the fastener has been fullyinserted in the ring and the insertion/extraction tool 114 has beenremoved. Shafts 124 of locking mechanism 116 are uncompressed, allowingprongs 126 to extend out of holes 108 in fastener head 102. Prongs 126extend into groove 132 on the ring 130.

To remove a threaded fastener 100 from ring 130, insertion/extractiontool 114 is inserted in the opening 104 in fastener head 102 to compressthe shafts 124 of the locking mechanism 116. Compressing the shafts 124causes the prongs 126 to retract through holes 108 and removes theconnection between the prongs and the ring 130. The tool 114 may then berotated to remove the fastener 100 from the bone.

After insertion of a fastener 100 and locking mechanism 116 into a bone,if the fastener 100 becomes loose within the bone, fastener backout fromthe bone plate may be resisted by the locking mechanism-grooveconnection between locking mechanism 116 and the ring 130. Thus, even iffastener shank 110 loosens within the bone, the fastener head 102 willtend to remain within ring 130 in the hole 24 of the plate 22. There maybe some freedom of movement in the connection between the prongs 126 andthe groove 130 to allow a fastener 100 to back out slightly from a boneafter insertion.

During the surgical procedure for attaching a bone plate to bones usingthe devices depicted in FIGS. 5-14, holes may be drilled and tapped intothe bones to which the bone plate 22 is to be attached. The bone plate22 may be positioned adjacent to the bones. Rings 130 may be positionedwithin each end hole 24 before or during the surgical procedure. Afastener 100, with a pre-inserted locking mechanism, may be positionedthrough a ring 130. An insertion/extraction tool 114 may be inserted inthe opening 104 of threaded fastener 100 to compress the lockingmechanism 116 within the cavity of the driver head of the tool.Compressing the locking mechanism 116 retracts the prongs 126 of thelocking mechanism within the fastener opening 104. The fastener 100 maythen be rotated to insert the fastener 100 into a bone. As the fastener100 is rotated, fastener head 102 moves into the ring 130. Movement ofhead 102 into ring 130 causes the ring to expand against the end hole 24to fix the fastener 100 relative to the plate 22. Once the fastener 100is fully inserted, insertion/extraction tool 114 is removed. Removingthe tool 114 causes the locking mechanism 116 to uncompress so that theprongs 126 extend through the holes 108 in the fastener head 102 andengage ring the groove 132 in the ring 130. Fasteners 100 may beinserted through the remaining end holes 24 and into bone to securelyattach the plate 22 to the bones.

FIG. 15 illustrates an embodiment of a fastener 200 with fastener head202 having groove 204. When a fastener 200 is inserted through a ring230 positioned in a plate 22, the groove 204 may engage fingers 232 onring 230 (the ring shown in FIGS. 19 and 20) to secure the fastener 200within the ring 230. Fastener 200 may include the head 202 and shank 206with threading 208. Head 202 may include opening 210 configured toaccept a driving tool.

The engagement of a finger 232 of a ring 230 on groove 204 may inhibitfastener 200 from backing out of the ring after insertion of thefastener into the plate 22. In an embodiment, the outer surface of head202 is substantially cylindrical. In another embodiment, as shown inFIG. 16, the head 202 may taper. The widest portion of the head 202 maybe near the top surface of the head, and the narrowest portion may benear the shank 206.

FIG. 17 illustrates an embodiment of a fastener 200 which has radialslots 212 extending from the outer surface of the head into the opening210. The radial slots 212 may allow a portion of head 202 to contractduring insertion. The radial slots 212 may also be used to engage aportion of a drive head of an insertion/extraction tool (not shown).

FIGS. 15, 16, and 17 illustrate fastener heads 202 wherein the grooves204 are rims along top edges of the heads. FIG. 18 illustrates anembodiment of a fastener 200 wherein the groove 204 is located at aposition along the side of the fastener head 202. The groove 204 may belocated at any position along the side of the fastener head 202. Whenthe fastener head 202 is driven through a ring 230, the interaction ofthe fastener head, the ring, and the end hole 24 allows fingers 232 ofthe ring to snap into the groove 214. The fingers 232 may secure thefastener head 202 to the ring 230.

FIGS. 19 and 20 show perspective views of embodiments of ring 230 thatmay be used with fasteners having a groove. Ring 230 may include bottom234, top 238, an outer surface 48, an inner surface 60, gap 36, andslots 240 and notches 242. The slots 240 and notches 240 may form thefingers 232. Gap 36 may allow ring 230 to contract. Contraction of thering 230 may facilitate the insertion of the ring into an end hole 24 ina bone plate 22. Gap 36 may also allow the ring 230 to expand againstthe end hole 24 when a fastener head 202 passes into the ring. Expansionof the ring against the hole 24 fixes the fastener 200 relative to thebone plate 22.

In some embodiments, outer surface 48 of the ring 230 may be textured toincrease the coefficient of friction between ring 230 and the hole 24.In some embodiments, inner surface 60 of the ring 230 may be tapered tomatch a tapered head of a fastener 200. Having tapered surfaces mayfacilitate the expansion of ring in an end hole 24 during insertion ofthe fastener into the bone plate system 20.

The shape of the end hole 24 may push the fingers 232 inwards past theedge of the groove 204 of a fastener 200 when the groove is insertedinto a ring 230 so that the groove passes an upper edge of the ringslots 240. The inward positioned fingers 232 may inhibit fastener 200from backing out of the ring 230 and the hole 24. When the fastener 200is inserted into the ring 230, the fastener head 202 may expand theoutside surface 48 of the ring against the inner surface 46 of the endhole 24 to fix the fastener 200 to the ring 230, and the ring to theplate 22.

FIG. 21 is a perspective view of an embodiment of a ring that may beused with fasteners 200 that have rims 204, such as the fasteners shownin FIGS. 15-17. Ring 430 may include bottom 432, top 434, outer surface48, inner surface 60, gap 36, notches 436, and ridges 438. Notches 436divide the ring 430 into segments or paddles 440. Notches 436 and gap 36may allow ring 430 to contract, facilitating the insertion of the ringinto a hole 24 of a bone plate 22. Notches 436 and gap 36 may also allowring 430 to expand when a fastener head 202 passes into the ring to fixthe position of the fastener relative to the bone plate 22. Notches 436may also allow paddles 436 to bend outwards during insertion of afastener 200. The outer surface 48 and/or the inner surface 60 may betextured. The inner surface of the ring 430 may be tapered to correspondto the taper of a fastener head 202.

FIG. 22 illustrates an embodiment of an insertion tool/extraction tool450 for use with a fastener 200 and ring 430. Insertion/extraction tool450 may include shaft 452, handle 454, driver head 456, and extractionmember 458. At one end of shaft 452 is handle 454 for turning the toolduring insertion and removal of a fastener 200. The illustration shows aT-handle, but any other type of handle that allows sufficient torque tobe applied to the fastener 200 to allow for insertion or removal of thefastener may be used. At the opposite end of shaft 452 from handle 454is driver head 456. The outer surface of driver head 456 may be shapedcomplementary to the shape of the opening 210 in the head 202 of thefastener 200.

The extraction member 458 shown in FIG. 22 may include grip 459, passage460, (shown in FIG. 23 c), tip 462, and extraction head 464. The passage460 extends through the grip 459 and the extraction head 464. During theinsertion process, extraction member 458 may be removed from shaft 452.To extract a fastener from a ring 430, extraction member 458 may be slidback on to shaft 452. Driver head 456 is inserted into the opening 210of the fastener 200. Extraction member 458 slides down shaft 452 untiltip 462 of extraction head 464 contacts the top of the ring 430.Downwards pressure on the extraction member 458 forces paddles 440 ofthe ring 430 outwards, and disengages the ridge 438 on the paddles 440from the rim 204 on the fastener head 202. The fastener 200 may then bebacked out of the plate 22 by rotating the shaft 452 with the handle454. Preferably, rotating shaft 452 does not rotate the extractionmember 458.

FIGS. 23 a, 23 b, and 23 c show partial cross sectional views of athreaded fastener 200, ring 430, and insertion/extraction tool 450during the insertion and extraction processes. Referring to FIG. 23 a,driver head 456 of insertion/extraction tool 450 is inserted in opening210 of fastener head 202. Ring 430 is positioned inside a hole 24 in abone plate and the bone plate is positioned on a bone (bone and boneplate not shown). Fastener 200 is screwed into the bone until the outersurface of fastener head 202 contacts the surfaces of the paddles 440.The tapering of the outer surface of fastener head 202 provides aramping force on the surfaces of the paddles 440, to bend the paddlesoutwards as fastener 200 is screwed farther into the bone.

In FIG. 23 b, fastener 200 has been screwed in to the desired depth.Fastener head 202 penetrates ring 430 far enough to allow ridges 438 tosnap onto rim 204 on fastener head 202. Driver head 456 ofinsertion/extraction tool 450 is shown still inserted in opening 210prior to removal from the opening. After insertion, if the fastener 200becomes loose within the bone, fastener backout from the bone plate maybe resisted by the ridge-rim connection between fastener head 202 andring 430. Thus, even if the fastener shank loosens within the bone, thefastener head 202 will tend to remain within ring 430 in the hole 24 ofthe plate 22 so as not to protrude from the plate into surrounding bodytissue. In some embodiments, there may be some freedom of movement inthe connection between the ridges 438 on the paddles 440 and the rim 204to allow a fastener 200 to back out slightly from a bone afterinsertion. Typically, the freedom of movement is limited so that thefastener head 202 may not protrude from the plate 22.

FIG. 23 c shows insertion/extraction tool 250 being used to remove afastener 200. Driver head 256 is inserted in opening 210 of fastener200. Extraction head 464 is slid down shaft 452 of insertion/extractiontool 450 until the sloped surface of tip 462 applies a wedging forceagainst the sloped upper surfaces of paddles 440. The wedging forcebends the paddles 440 outwards to disengage the ridges 438 from the rim204. Fastener 200 may then be backed out of the bone, the ring 430 andthe plate 22.

The plate, fasteners, and locking mechanisms may be made of steel (e.g,stainless steel), titanium, steel alloys or titanium alloys. Thesematerials are generally nontoxic, bio-compatible, strong, andnon-corrosive. Other materials that have these properties may also beused. The plate and the rings may be made of a number of bio-compatiblematerials including metals, plastics, and composites.

Any of the embodiments described above may be used individually or incombination with other embodiments described above. Furthermodifications and alternative embodiments of various aspects of theinvention will be apparent to those skilled in the art in view of thisdescription. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as examples of embodiments. Elements and materials maybe substituted for those illustrated and described herein, parts andprocesses may be reversed, and certain features of the invention may beutilized independently, all as would be apparent to one skilled in theart after having the benefit of this description of the invention.Changes may be made in the elements described herein without departingfrom the spirit and scope of the invention as described in the followingclaims.

1. A spinal plating system comprising; an elongated plate having aplurality of bone screw apertures; a locking ring disposed in one of thebone screw apertures, the locking ring having at least a portionresiliently expandable from a retracted state to an expanded state; abone screw inserted into the one of the bone screw apertures, the bonescrew having a head with a diameter sized such that in the retractedstate the locking ring prevents the bone screw from backing out of theplate and in the expanded state the locking ring permits insertion andremoval of the bone screw relative to the one bone screw aperture; and atool for removing the bone screw from the one bone screw aperture, thetool having a first portion coupled to the head of the bone screw and asecond portion resiliently expanding the locking ring to the expandedstate.
 2. The spinal plating system of claim 1, wherein the firstportion is threadably engaged with the head of the bone screw.
 3. Thespinal plating system of claim 1, wherein the first portion comprises ahex section that complements a hex tool opening in the bone screw. 4.The spinal plating system of claim 1, wherein the locking ring comprisesa plurality of paddles.
 5. The spinal plating system of claim 1, whereinthe head of the bone screw comprises a ledge.
 6. The spinal platingsystem of claim 1, wherein the first portion is independently rotatablerelative to the second portion.
 7. A method of surgically repairing bonewith an elongated plate having a plurality of bone screw apertures, themethod comprising: locating a locking ring in one of the bone screwapertures, the locking ring defining a locking ring opening and beingresiliently expandable from a retracted state to an expanded state suchthat the locking ring opening has a first opening diameter in theretracted state and a second, larger opening diameter in the expandedstate; inserting a bone screw into one of the bone screw apertures, thebone screw having a head with a head diameter greater than the firstopening diameter and less than the second opening diameter; and removingthe bone screw from the one bone screw aperture with a tool having afirst portion engaging the head of the bone screw and a second portionresiliently expanding the locking ring to the expanded state.
 8. Themethod of claim 7, wherein the tool having the first portion threadablyengages the head of the bone screw.
 9. The method of claim 7, whereinthe first portion comprises a hex portion, and inserting the hex portioninto a complementary hex indention in the bone screw.
 10. The method ofclaim 7, wherein engaging the head of the bone screw with the firstportion of the tool includes the step of threadably engaging aninternally threaded aperture of the head.
 11. The method of claim 7,further comprising rotating the at least one bone screw with the firstportion of the tool.
 12. The method of claim 7, further comprisingdrawing the second portion downward to resiliently expand the lockingring to the expanded state.
 13. A system for surgically repairing bone,the system comprising: an elongated plate having a plurality of bonescrew apertures; a locking ring disposed in one of the bone screwapertures, the locking ring defining a locking ring opening and beingresiliently expandable from a retracted state to an expanded state suchthat the locking ring opening has a first opening diameter in theretracted state and a second, larger opening diameter in the expandedstate; a bone screw inserted into the one of the bone screw apertures,the bone screw having a head with a diameter greater than the firstopening diameter and less than the second opening diameter; and a toolfor removing the bone screw from the one bone screw aperture, the toolhaving a first portion for engaging the head of the bone screw and asecond portion for resiliently expanding the locking ring to theexpanded state.
 14. The system for surgically repairing bone of claim13, wherein the first portion of the tool threadably engages aninternally threaded aperture provided in the head of the bone screw. 15.The system for surgically repairing bone of claim 13, wherein the firstportion of the tool engages a hex opening in the head of the bone screw.16. The system for surgically repairing bone of claim 13, wherein thesecond portion of the tool includes a hollow cylindrical membersurrounding the first portion.
 17. The system for surgically repairingbone of claim 13, wherein the second portion includes a tip having awedge portion configured to expand the locking ring.
 18. The system forsurgically repairing bone of claim 13, wherein the first portion isindependently rotatable relative to the second drive portion.
 19. Thesystem for surgically repairing bone of claim 13, wherein the lockingring comprises a plurality of paddles.
 20. The system for surgicallyrepairing bone of claim 13, wherein the bone screw comprises a ledge.